The present invention relates to an electrical-steel-sheet formed body for a rotor core, a rotor, a rotary electric machine and a related method, and, more particularly, to an electrical steel sheet formed body for a rotor core of a built-in permanent magnet type rotary electric machine, a rotor using such a formed body for a built-in permanent magnet type rotary electric machine, a built-in permanent magnet type rotary electric machine using such a formed body, and a method of manufacturing an electrical-steel-sheet formed body for use in a rotor core of a built-in permanent magnet type rotary electric machine.
Built-in permanent magnet type rotary electric machines have heretofore been employed, for example, in electric vehicles and hybrid automobiles as drive motors. Among these, since synchronous motors in each of which permanent magnets are built in a rotor can be realized in high speed rotating capabilities, miniaturizations and light weights, the synchronous motors have many applications.
FIGS. 29 and 30 are views illustrating rotor cores for built-in permanent magnet type synchronous motors.
In FIGS. 29 and 30, both the rotor cores 100 have eight poles, with one magnet-insertion opening 101 being formed for one pole. Such a rotor core 100 is formed first by stamping an electrical steel sheet in a core shape as shown and then stacking a plurality of resulting thin plates in a direction perpendicular to a sheet of the figure. In the current specification, a sheet of thin plate forming the rotor core is referred to as an electrical-steel-sheet formed body because the thin plate is formed from the electrical steel sheet.
By the way, in usual practice, the motor can be miniaturized when rotated at a high speed. For this reason, attempts have heretofore been made in the past to develop the motors that have high speed rotating capabilities. However, when the rotor of such a built-in permanent magnet type motor rotates, the rotor develops a centrifugal force that is exerted to the magnets and increases as the rotational speed increases. Thus, the maximum rotation speed of the motor is limited to the strength of the electrical steel sheet per se used for the rotor.
On the contrary, the higher strength of the electrical steel sheet, the larger will be iron loss, with resultant heat being developed in the rotor. For this reason, even though the strength of the rotor is desired to increase, but a difficulty is encountered. This is because, if the rotor develops heat, the magnet loses a magnetic force due to resulting heat depending on the magnet which is used and, so, the temperature rise of the rotor must be avoided.
Japanese Patent Application Laid-Open Publication No. 2001-16809 discloses a technology related to a shape of a magnet-insertion opening that enables a stress concentration, occurred in a rotor core caused by a centrifugal force, to be dispersed in a wide area in order to provide high speed rotating capability of the rotor without the need for increasing iron loss of an electrical steel sheet.
In particular, as shown in FIGS. 31 and 32, attempts are made to form circular arc spaces 102 (see FIG. 31), 105 (see FIG. 32) that involve corners of magnet-insertion openings (slots) 101 where stresses are to be concentrated due to centrifugal forces and have larger radii of curvatures than those of the corners, in such a manner that the circular arc spaces 102, 105 function to dislocate the stress concentrations in the shortest areas between the outer peripheries 110 and the slots 101. Such a structure may resultantly allow the stress concentrations to be dispersed and alleviated.
Further, “Development of Stress Improvement Technique Using Pulse Laser Irradiation-Evaluation of Stress Improvement for Type 304 Stainless Steel” (By Minoru Oda, et al, “Material” Vol. 49, No.2, pp. 193-199, Issued on February, 2002) discloses a laser peening technology.